Apparatus and method for television transmission



June 20, 1939.- 2,163,545

APPARATUS AND memos FOR TELEVISION TRANSMISSION s CLOTHIER' ET AL FiledAug. 51, 1937 Patented .iso, 1939 'rus Amr- METHOD son TELE- vrsronTRANSMISSION Stewart nominee, llrvin'gtor and name o.

Hogencamp, ,Maplewood, N. 3., asslgnors to Kolorama laboratoriescorporation of New ilersey Inc Newark, N. 3., 2.

Application August 31, 1937, Serial No. 161,730.

7 Claims (oi. its-v.3)

Our invention relates to improvements in anp atus and methods fortelevision transmission.

' While the various-apparatus and methods proposed heretofore fortelevision transmission have been effective to transmit a recognizablepicture atleast ovenairelatively short distance, each of the same hasbeen found to involve necessarily intrinsic structural ch 'racteristicsand principles giving rise to problems ofmanufacture and, generally,definite limitations in the way of detail of the image reproduced at thereceiving station, and output level of the picture signals produced bythe transmitting apparatus for a given intensity the view or subjectbeing tele-,

size, the uniformity of photosensitivity of the 30 particles over theentire mosaic surface or area, and the prevention of leakage betweenadjacent particles. These. requirements in the television transmittingapparatus of this general type give the same the definite limitationsreferred to.

In television transmission apparatus of the general type disclosed inPatent No. 1,773,980 issued to Philo T. Farnsworth, there isnorequirement for a mosaic, photosensitive screen, but there is, however,0 fiection in horizontal and vertical directions, of

electrons issuing simultaneously. from the individual eementatl areas ofa photosensitive screen, with respect to a single, remote and relativelyminute anode disposed on the far side of a small 45 aperture in ametallic plate. Suchapparatus has been found' to involve problems due to00: curring distortion of the electron stream, and the fact that eachofthe individual rays of electrons making up the entire stream isnotfocused per-. 50 fectlyon theanode as the stream is deflectedforscanning.

with the foregoing inmind, an object, of our invention is the provisionof an improved apparatus and method for television transmission which 55avoids the difl lculties referred to,

and: by which a detail or picture definition the requirement forsimultaneous .de-

' mica or glass.

substantially greater output level of picture signal can be obtained,for a given intensity of illumina-v tion of the view or subject beingtelevised and for. a given amount of signal amplificationat'thetransmitter, than has been possible with the various apparatus andmethods proposed heretofore for the same purpose.

Other objects and advantages will hereinafter appear.

Our invention resides in the improved construction and method of.operation hereinafter described and claimed.

Forthe purpose of illustrating our invention, an

embodiment thereof is shown in the drawing,

wherein:

Figure l is a simplified, diagrammatic view of television transmissionapparatus constructed and operating in accordance with our invention;

Figure 2 is an enlarged, fragmentary, sectional view, the section beingtaken on the line 2-2 in Fig.1; and

Figure -3 is a view similar to Fig. 1, modification.

In the drawing, the reference numeral ill designates an evacuated tubeprovided at an end 'thereof with a photosensitive screen ii. The

screen I i may be formed onthe inside surface of the transparent endwall of the tube; and be in the form of a continuous, semi-transparentcoating of silver over which is silver oxide and'cesium, as will be-wellunderstood by those skilled in the art. As an alternative, the screen itmay be in the formof a wire screen of fine mesh, photosensitized andsupported within the tube in spaced relation with respect to theadjacent end wall thereof. I

At its opposite end, the tube i0 is providediwith means, in the form ofa gun l2'of a suitable conventional construction, for developing a rayit of electrons, directed at and focused on a screen M; The screen it issupported between the photosenshowing. a

sitive screen H and the gun l2, and the edge thereof is at east slightlyspaced from thewall of the tube.

The screen I4 is. imperforate, that is, there are no apertures oropenings in the eifectlv'e or operating area of the same, and at leastthis area is' made entirely also be the axisof the tube, is a singleanode l5 of elemental 'size compared to the areas of the of insulatingmateriahsuch as line through the respective screens. Asshownin Fig. 2,the anode i5 may be in the form of a small'wire loop formed from the endof a supporting and'connecting wire I6 which may be encased in a glassstem I'I extending radially inwardly from the wall of the tube.

An electrode -I8, which may be in the form of a metal ring. is supportedadjacent to and on the gun side of the screen I4. A similar electrode I9A saw-tooth voltage wave at line frequency is supplied by a generator 20and impressed across deflecting plates ii. A saw-tooth voltage wave.

at the frame frequency is supplied by a generator 22 an'd impressedacross deflecting plates 23. In this way, the ray I3 of electrons isdeflected simultaneously in horizontal and vertical directions to causeit to scan the adjacent surface of the screen I I in a conventionalmanner.

Synchronizing and framing signals are also supplied by the generators2.0 and 22, respectively; and after amplification by a common. amplifier24 are fed to a modulator 25 and thence to the transmitter 26.

A light image of the view or subject 21 for transmission isiocused by asuitable lens system 28 on the adjacent surface of the semitransparent,photosensitive screen II.

In operation, the anode I5 and the electrodes I8 and I9 are maintainedat potentials positive with respect to the potential of the screen II,and the potentials of the anode I5 and the electrode I8 are positivewith respect to the poten tial of the electrode I9, as represented inthe Y drawing. It will 'be'understood that for anyparticular conditionof operation, adjustments will be made to place the respectivepotentials of the anode I5 and the electrodes I8 and I9 at the valuesfor most efficient operation. As an example, the potential of the anodeI5 with respect to that of the screen II might be of the order of 1,000volts positive.

In explaining the manner in which our im proved apparatus is believed tooperate, the electrical action at only one of the minute, elementalareas or points 29 of the entire eflective portion of the photosensitivescreen II, will first be considered. Electrons are emitted from thepoint 29 in amount corresponding to the intensity, at the instant, ofthe light ray 30 coming from the corresponding point of the subject 21,and the amount of electronic emissionvaries lnstantaneously with anddirectly proportionally tooccur ring variations in intensity of thelight, ray 30. At any instant, the electronic emission directly at thephotosensitive point 29'takes place in many different directions and ina more or less hap-'-' hazard fashion. However, the strong attraction ofthe anode I5 for the electrons causes them to fall in line and'travel a'common, straight path 3|, at high velocity, to the anode I5. Some of theelectrons will be absorbed by or passed to ground by way of the anodeI5, but the remainder, still at a relatively high velocity, will pass onthrough thepinhole aperture 32 in'the anode and continue along thestraight path 3| to the complementary or corresponding elemental area orpoint 33 of the adjacent surface of the screen I4,

, whereupon an electrostatic charge is developed or induced ontheopposite side ofthe screen 14, directly opposite the point 33. Suchelectrostatic charge, like the-original electronic emission from thepoint 29 of the photosensitive screen I I, corresponds in value to theintensity, at the instant,

, electrode I8.

"operating action. By variation to a maximum. Similar electrodes of thelight ray 30, andvaries instantaneouslywith and directly proportionallyto occurring variations in intensity of the light ray 30.

When the electron ray I3, the intensity of which is constant, strikesthe screen I4 at the point 33 during the scanning action, theelectrostatic charge referred to is instantaneously neutralized bytheelectrons of the ray, but only such number of electrons are taken orabsorbed from the ray as is required to neutralize the charge. Theremainder of the electrons of the ray I3 are collected by theelectrodeI8 and cons'titute the picture current or picture signal for thatparticular point of the subject 21 being analized at the instant.

The. picture signals are'taken from the collector electrode I8 byaconnection 34 and supplied to a picture-signal amplifier 35, fromwhence they pass to the modulator 25 and the transmitter 26.

The electrical action at each of the other minute, elemental areas orpoints of the entire effective portion of the photosensitive screen IIis 1, are designated by the same respective'reference numeralsas thelatter. In this case, however, the electron gun I2 and the collectorelectrodeI8 are on the same side of the screen I4 as the photosensitivescreen' II, and neutralization of the electrostatic charges by theelectrons of the. scanning ray I3 takes place on this side of the screenI4. Also, the screen I I is backed by a supporting metallic plate 36from which the picture signals may be taken instead of from the d Thearrangement and operating action, otherwise, is similar to that in Fig.

In Fig. 3, oppositely directed, conical electrodes 31 and 38 are shownon opposite sides of the anode I5, and both are maintained at potentialspositive with respect to that of the screen I4.

The potential of either or both oi the electrodes 31 and 38 may bnegative with respect to that of the anode I5. While use oftheelectrodes 31 and 38 is not essential, it is seen thattheelectricalinfluence of the same might improve the of the respectivepotentials on the electrodes ,3! and 38, the size of the electrostaticimage on the adjacent surface of the screen I4 may be controlled, and,also, the

numberof effective electrons reachingthis surface by way of the aperture32 may be met be embodied in the construction shown inFig. 1.

aspect thereof, it will be seen that this resides in a new method ofoperation in which electrons, emitted from the individual, elementalareas or points of the entire effective portion of aphotosensitivescreen, are caused to converge-simultaneously towarda'common focal regio r fjremote from such screen, this region in theembodiment disclosed being that immediately at or about the anode I5.Also, in our new method of operation,

Considering our invention from thebroader electrons are caused to traveltoward the respective, individual elemental areas or points of theentire effective portion of a screen, such as the screen It, andsimultaneously in paths diverging irom a common focal region remote fromthis screen.

Furthermore, in our new method of operation, it will be seen thatelectrons are caused to travel from any one, individual, elemental areaor point of a first screen, such as the point 29, toward a correspondingelementalarea or point of a second screen, such as the point 33, andalong paths which substantially intersect the respective paths ofsimultaneous and similar travel of electrons from the other individual,elemental areas or points of the first screen.-

Another important aspect of our invention resides in the operating stepwherein electrical conditions occurring at the individual, elementalareas or points of the entire portion of a screen, such as thephotosensitive screen II, are simultae neously utilized to produce, atthe respective and corresponding individual, elemental areas or pointsof the entire portion of a second screen,

such as the screen [4, electrical conditions correspondingrespectivelyin value to said firstmentioned electrical conditions.

As to the construction of our improved appa-' ratus, it will be seenthat this does not embody the undesirable mosaic screen to be found insome of the various constructions of television transmitting tubesproposed heretofore, and, furthermore, avoids the various diflicultiesof manufacture and operation referred to before.

It will be understood that various modifications, such as in the size,shape and arrangement of" the parts, are possible without departing fromthe spirit of our invention or the scope of the claims.

We claim as our invention: I

1. In apparatus for television transmission, a

photosensitive screen, a second screen, means for causing the travel ofelectrons from each individual elemental area of said first screentoward a corresponding elemental area of said second screen andalong apath which substantially intersects the respective paths of simultaneousandsimilar travel of electrons from all other individual elemental areasof said'flrst screen at a common focal point intermediate said screens,aind means including a cathode ray gun structure for scanning saidsecond screen with an electron beam to develop picture signals.

2. In apparatus for television transmission, a photosensitive screen, asecond screen, a single ring anode of minimum surface area with anaperture of elemental sizecompared' to the respective areas of saidscreen, said anode bein disposed intermediate said screen andsubstantially on a line through the respective centers of said screens,and means including a cathode ray gun structure for scanning said secondscreen to develop picture signals.

3. In apparatus for television'transmission, a photosensitive screen, asecond screen of insulating material, a single apertured ring anode ofelemental size compared to the respective areas of said screens, saidanode being disposed intermediate said screens and operating to effecttravel of electrons from the individual elemental areas of saidphotosensitive screen to the respective and-corresponding elementalareas of said second screen and simultaneously along paths whichintersect in the region of said anode, means including a cathode-ray gunstructure for developing a ray of electrons and directing the same atsaid second screen, and means for deflecting said ray to cause the sameto scan said second screen.

4. In apparatus for television transmission, a photosensitive screen, asecond and imperforate screen ,at least the eflective portion of whichis entirely of insulating material, a single centrally apertured anodeof elemental size compared to the respective areas of said screens, saidanode being disposed intermediate said screens and sub-' stantially on aline through the respective centers of said screens, means including acathode-ray gun structure for developing a ray of electrons anddirecting the same at said second screen,

means for deflecting said ray to cause the same to scan said secondscreen, and an electrode disposed between said second screen and saidray-deflecting means.

5. In apparatus for television transmission, a tube provided at one endthereof with a photosensitive screen substantially perpendicular to theI corresponding elemental areas of said secondnamed screen and alongpaths which intersect said axis at a common focal point, and means fordeflecting said ray of electrons to cause the same to scan saidsecond-named screen.

6. In apparatus for television transmission, a tube provided at one endthereof with a photosensitive screen substantially perpendicular to thelongitudinal axis of'the tube, a lens system for projecting onto saidscreen a light image of the subject for transmission, an electron gun atthe other end of said tube for developing a ray of electrons, a screendisposed in said tube between and spaced from the photosensitive screenand said gun and being substantially perpendicular to said axis, saidsecond-named screen consisting entirely of imperforate insulatingmaterial at least in the operating area thereof, means disposed betweensaid screens and operating to effect travel of electrons from theindividual elemental areas of said photosensitive screen to therespective and corresponding elemental areas of said second-named screenand simultaneously along paths each of which intersects said axis at acommon focal point, and means for deflecting said ray of electrons tocause the same to scan said second-named screen.

7. In a television transmitter tube including a photosensitive screen atone end,

- a second.screen of imperforate insulating material spaeed from saidfirst screen, means intermediatejsaid screens for causing electronsemitted from said photosensitive screen to travel to said second screen,'and means including a. cathode-ray gun structure for scanning saidsecond a cathode-ray I screen with an electron beam to develop picturesignals.

STEWART L. CLO'I'HIER. HAROLD C. HOGENCAMP.

